1. Field of the Invention
This invention relates to polymerization catalyst systems employing oxalic acid diamides as a modifier, to methods of making such polymerization catalyst systems, and to polymerization processes for producing polyolefins, particularly polypropylene, which exhibits substantially higher sterospecificity than catalyst systems without oxalic acid diamides modification.
2. Description of the Related Art
Ziegler-Natta catalyst systems for polyolefin polymerization are well known in the art. Commonly, these systems are composed of a solid Ziegler-Natta catalyst component and a co-catalyst component, usually an organoaluminum compound. To increase the activity and sterospecificity of the catalyst system for the polymerization of α-olefins, electron donating compounds have been widely used (1) as an internal electron donor in the solid Ziegler-Natta catalyst component, and/or (2) as an external electron donor to be used in conjunction with the solid Ziegler-Natta catalyst component and the co-catalyst component.
In the utilization of Ziegler-Natta type catalysts for polymerizations involving propylene or other olefins for which isotacticity is a possibility, it may be desirable to utilize an external electron donor, which may or may not be in addition to the use of an internal electron donor. Acceptable external electron donors include organic compounds containing O, Si, N, S, and/or P. Such compounds include organic acids, organic acid esters, organic acid anhydrides, ethers, ketones, alcohols, aldehydes, silanes, amides, amines, amine oxides, thiols, various phosphorus acid esters and amides, etc. Preferred external electron donors are organosilicon compounds containing Si—O—C and/or Si—N—C bonds, having silicon as the central atom. Such compounds are described in U.S. Pat. Nos. 4,472,524; 4,473,660; 4,560,671; 4,581,342; 4,657,882; 5,106,807; 5,407,883; 5,684,173; 6,228,961; 6,362,124; 6,552,136; 6,689,849; 7,009,015; 7,244,794; 7,276,463; 7,619,049; 7,790,819; 8,247,504; 8,648,001; and 8,614,162, which are incorporated by reference herein.
Common internal electron donor compounds, which are incorporated in the solid Ziegler-Natta catalyst component during preparation of such component, are known in the art and include ethers, ketones, amines, alcohols, heterocyclic organic compounds, phenols, phosphines, and silanes. It is well known in the art that polymerization activity, as well as stereoregularity, molecular weight, and molecular weight distribution of the resulting polymer depend on the molecular structure of the internal electron donor employed. Therefore, in order to improve the polymerization process and the properties of the resulting polymer, there has been an effort and desire to develop various internal electron donors. Examples of such internal electron donor compounds and their use as a component of the catalyst system are described in U.S. Pat. Nos. 4,107,414; 4,186,107; 4,226,963; 4,347,160; 4,382,019; 4,435,550; 4,465,782; 4,522,930; 4,530,912; 4,532,313; 4,560,671; 4,657,882; 5,208,302; 5,902,765; 5,948,872; 6,048,818; 6,121,483; 6,281,301; 6,294,497; 6,313,238; 6,395,670, 6,436,864, 6,605,562; 6,716,939; 6,770,586; 6,818,583; 6,825,309; 7,022,640; 7,049,377; 7,202,314; 7,208,435; 7,223,712; 7,351,778; 7,371,802; 7,491,781; 7,544,748; 7,674,741; 7,674,943; 7,888,437; 7,888,438; 7,935,766; 7,964,678; 8,003,558; 8,003,559; 8,088,872; 8,211,819; 8,222,357; 8,227,370; 8,236,908; 8,247,341; 8,263,520; 8,263,692; 8,288,304; 8,288,585; 8,288,606; 8,318,626; 8,383,540; 8,536,290 8,569,195; 8,575,283; 8,604,146; 8,633,126; 8,692,927; 8,664,142; 8,680,222; 8,716,514 and 8,742,040, which are incorporated by reference herein.
Most commercial propylene polymerization catalysts currently used employ alkyl phthalate esters as an internal electron donor. However, certain environmental issues have been recently raised concerning the continued use of phthalate derivatives in human contact applications. As a result, the employment of a phthalate-free propylene polymerization catalyst or a catalyst system that employs a reduced amount of phthalate is now necessary for the production of polypropylene to remedy these issues.
U.S. Pat. No. 6,323,150 describes the use of a propylene polymerization catalyst which contains a reduced amount of phthalate as an internal electron donor. However, the resulted polypropylene product was found to exhibit low isotacticity and productivity. This prior art also teaches a polymerization catalyst consisting of a polyether compound combined with the phthalate derivative as internal electron donors. The resultant polypropylene product exhibits lower isotacticity than that of a catalyst containing only the phthalate derivative.
U.S. Pat. No. 7,491,781 teaches the use of an internal electron donor in a propylene polymerization catalyst component which does not contain a phthalate derivative. However the resultant propylene polymerization catalyst produced polypropylene with lower isotacticity than that of a catalyst containing a phthalate derivative.
As such, there is still a need for developing catalyst systems that can be used to produce polyolefins, particularly polypropylene, containing a reduced amount of phthalate derivatives as internal electron donors while exhibiting high isotacticity. Even more desirable is the development of a phthalate-free catalyst system capable of producing polypropylene with an isotacticity that is equal to or better than systems that contain only phthalate derivatives.